Principal Investigator: Durham, Paul Louis PROJECT SUMMARY/ABSTRACT The long-term goals of our proposed studies are to understand the mechanisms by which known risk factors promote persistent sensitization of trigeminal neurons leading to chronic orofacial pain conditions, and testing novel therapeutic strategies to prevent or reverse the sensitized state of trigeminal nociceptors. Temporomandibular joint disorders (TMDs), which involve inflammation and pain in the joint or muscles of mastication, are the most common chronic orofacial pain and are the second most commonly occurring musculoskeletal conditions resulting in pain and disability, with an annual cost estimated at $4 billion. While about half to two-thirds of those with TMDs will seek treatment, approximately 15% will develop chronic TMD. Based on findings from the NIDCR-funded OPERRA study, prolonged jaw opening, neck muscle tension/inflammation, and female gender are risk factors that increase the likelihood of developing TMD, presumably by promoting persistent peripheral and central sensitization of trigeminal nociceptive neurons. In support of this notion, we have found in preliminary studies that prolonged jaw opening, which can occur during a routine dental procedure, resulted in a sustained level of mechanical sensitization of trigeminal nociceptive neurons in male rats that did not resolve for 14 days. Interestingly, we discovered that neck muscle inflammation prior to jaw opening resulted in a more prolonged period of mechanical sensitization that persisted beyond 14 days, and furthermore, the duration and level of sensitization was greater in female rats. We have found in our preliminary studies that neck muscle inflammation promotes in the spinal trigeminal nucleus (STN) an increase in the levels of the neuropeptide calcitonin gene-related peptide (CGRP), signaling protein PKA, and microglial protein Iba1, which are proteins implicated in central sensitization. In a published study, we provided evidence that inclusion of grape seed extract (GSE) as a dietary supplement decreased CGRP expression in the STN and increased levels of the anti-inflammatory protein MKP-1 in neurons and glia, and therefore may function to inhibit development of peripheral and central sensitization. Thus, based on results from our published and preliminary studies, we will test the hypothesis that reported TMD risk factors promote cellular changes in trigeminal neurons and glial cells to initiate and maintain a hyperexcitable state of nociceptive neurons characteristic of peripheral and central sensitization and that dietary supplementation with GSE will inhibit TMD pathology. To test our hypothesis, in Aim 1 we will correlate temporal changes in nocifensive sensitivity to mechanical stimulation of primary trigeminal neurons to psychosocial behavioral changes in response to multiple TMD risk factors. In Aim 2, we will utilize immunohistochemistry and qPCR to investigate changes in key proteins, including gap junction connexins, implicated in the development of peripheral and central sensitization mediated by the TMD risk factors. In Aim 3, we will investigate the mechanisms by which inclusion of GSE as a dietary supplement can prevent and/or reverse ongoing trigeminal nociceptor sensitization mediated by TMD risk factors. We predict that multiple TMD risk factors will be associated with a more severe phenotype characterized by sustained trigeminal sensitization and negative psychosocial behaviors, and provide evidence to support the use of GSE as a novel nutraceutical for managing TMD pathology. 1